1. Field of the Invention
The present invention relates to an audio amplifier, and more particularly, to an audio amplifier capable of performing self-oscillation.
2. Description of the Prior Art
Current conventional audio amplifiers are primarily implemented with Class D amplifiers. A conventional Class AB amplifier generates linear signals whereas a Class D amplifier generates pulse width modulation (PWM) signals, which primarily consist of audio signals, PWM activate signals, and harmonic waves. When a Class D amplifier operates, an output stage metal oxide semiconductor filed-effect transistor is switched from having a high resistance to a low resistance. Moreover, the Class D amplifier takes a significantly small duration in each cycle to operate under an active region, and therefore, the output stage power consumption of the Class D amplifier is far lower than the output stage power consumption of the Class AB amplifier. Besides, a LC filter, which has inductors and capacitors, stores enough power during an active region of each cycle of the Class D amplifier so that the stored power is not exhausted in each cycle by the power consumption of a speaker driven by said Class D amplifier.
However, while a plurality of Class D amplifiers is utilized in the same circuit at the same time, unnecessary noise is generated if output audio signals of said plurality of Class D amplifiers are asynchronous with each other so that a related audio output quality is significantly decreased. Moreover, under the circumstance that an operating frequency of a Class D amplifier is not properly manipulated, the Class D amplifier is easily disturbed by other noise having a similar frequency with said operating frequency of the Class D amplifier. When it is required to output audio signals from a Class D amplifier continuously, inputting audio signals into said Class D amplifier easily leads to a distortion of a previously inputted audio signal of said Class D amplifier, and leads to an entire decrease of output audio quality of said Class D amplifier.